Default theme Layouts are customized via WordPress Administration Panel
Widgets as WordPress Sidebars although they are not sidebars in fact.
The default layouts are:
All this layouts are represented as sidebars in the WordPress Administration Panel
The general approach for creating the Default Layout is to add the Page Builder widget to the sidebar then add other widgets inside Page Builder. Theme have some special widgets for creating Default Layouts. Please read descriptions inside sidebars about widgets that should be used for this purpose.
To import or restore demo content for Default Layouts in the WordPress Administration Panel open
Appearance / Import Demo Content, select Media Items and Appearance Widgets to import, then run import. Default Layouts will be imported with options for images, only if Media Items are selected for import also. If Media Items have already been imported, the existing items will be skipped, but Default Layouts will have image settings. Otherwise Default Layouts will be displayed without images.